Copolymers of olefinically unsaturated monomers are very well known. For example, copolymers of ethylene and another alpha-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and the like are readily available. Other monomers which have been polymerized with ethylene and/or alpha-olefins include acrylic acid, alkyl acrylates, methacrylic acid, vinyl acetate, acrylonitrile and carbon monoxide.
Two primary types of olefin polymerization techniques are used commercially for preparing high molecular weight olefin polymers and copolymers. One technique involves coordination catalysts of the Ziegler or Phillips type and include variations of the Ziegler type, such as the Natta type. The catalysts may be used at very high pressure, but may also be used (and generally are) at very low or intermediate pressures. The products made by these coordination catalysts are generally known as linear polymers because of the substantial absence of branched chains of polymerized monomer units pendant from the main polymer backbone. The other commercially-used technique involves very high pressure, high temperature, and the use of a free radical initiator, such as a peroxide. These polymers contain branched chains of polymerized monomer units pendant from the main polymer backbone. Such a technique has been employed to prepare high molecular weight, uniformly random copolymers of ethylene and acrylic or methacrylic acid as is described in U.S. Pat. No. 4,351,931. These methods have worked very well and are commercially attractive with such monomers as ethylene and acrylic acid; however, when more reactive monomers, such as styrene are copolymerized with ethylene, the rate of reaction has been difficult to control and the methods have not generally been used with such highly reactive species.
Vinyl pyridine homopolymers and copolymers are also widely known. As summarized in Vinyl and Diene Monomers, Part 3, E. C. Leonard (Ed.), Wiley-Interscience, (New York 1971) vinyl pyridines have been copolymerized with various monomers, including acrylamide, acrylonitrile, butadiene, butyl acrylate, chloroprene, diallyl ether, 2,5-dichlorostyrene, ethyl acrylate, isoprene, isopropenal acetylene, methacrylic acid, methyl acrylate, methyl methacrylate, phenylacetylene, styrene and vinyl acetate. Homopolymers and copolymers of vinyl pyridines generally have the same mechanical properties as styrene homopolymers and copolymers; however, because styrene is much less expensive, vinyl pyridine polymers are used commercially only in specialty applications such as cord dips for the tire industry, with acrylic fibers to improve dye receptivity, emulsifiers for polymerizations in acidic media, anion exchange resins, polyelectrolytes, and in photographic emulsions.
Vinyl pyridine homopolymers and copolymers have been prepared by free-radical and anionic methods. The free radical polymerization techniques have included liquid-phase free-radical polymerization, emulsion polymerization, radiation-induced polymerization and coordination polymerization. It has also been known to prepare block and graft copolymers of vinyl pyridines with various backbone polymers such as, for example, polyethylene, polypropylene and polybutadiene.